1. Field of the Invention
The present invention generally relates to computer systems having DDR SDRAM memory and, particularly to a novel apparatus and method for monitoring the DDR dynamic eye and improving the memory interface based on the data eye monitoring.
2. Description of the Prior Art
With the advent of high speed external memories that employ a source synchronous interface it has become difficult to extract data from the interface. Today DDR SDRAMs deliver data and strobe that are edge aligned. In order to capture the data, the strobe signal is delayed to the midpoint of the data and then used as a clock to latch the data into storage elements (i.e., the latches on a chip). With higher memory interface speeds, the amount of data eye available to move the strobe into is shrinking. For analysis and for strobe centering it would be advantageous to be able to determine the data eye internal to the chip.
U.S. Pat. No. 7,165,185 discloses a DDR II write data capture calibration tool that controls the rate with which data is input to a DRAM relative to an external DRAM clock. In the embodiments described, a known data pattern is used at each of the data inputs and the data is delayed across a clock. The data is delayed such that the predetermined pattern is recognizable and further delay adjustments are made until the predetermined pattern is no longer recognized indicating that an edge of the eye of the data is near a clocking edge of the clocking signal. The data delay is further adjusted to situate the position of the clock edge near the center of the data eye.
It would thus be highly desirable to provide an improved method for monitoring the DDR memory data eye and adjusting the strobe location to improve the memory interface.
It would be further highly desirable to provide a system and method for providing an infinite persistant data eye wherein the strobe signal may be continuously adjusted in real-time operation to ensure accurate latching of the data signals at the input of a receiving data latch circuit throughout its operation.